JP7437633B2 - Fuel cell cathode catalyst layer and fuel cell - Google Patents

Description

The present disclosure relates to a cathode catalyst layer of a fuel cell and a fuel cell.

A fuel cell includes a membrane electrode assembly having an electrolyte membrane and a pair of electrodes sandwiching the electrolyte membrane. Each of the pair of electrodes includes a catalyst layer and a gas diffusion layer in this order from the electrolyte membrane side.

As for the structure of the catalyst layer, Patent Document 1 describes secondary particles formed by a plurality of primary particles of carbon supporting a platinum catalyst, which penetrates into the inside of the secondary particles and covers the outside of the secondary particles. A catalyst layer containing an ionomer and having secondary particles having a radius in the range of 105 nm to 200 nm is described. Further, the ratio (I/C) between the mass I of the ionomer and the mass C of carbon in the catalyst layer is set to 0.65 to 1.35.

Further, in Patent Document 2, the catalyst layer includes a catalyst layer and a polymer electrolyte, and the catalyst layer contains a fibrous material that has hydrophilicity or whose surface has been treated to be hydrophilic.

In Patent Documents 1 and 2, the ionomer and the polymer electrolyte have proton conductivity. However, since moisture is required for proton conduction, fuel gas or oxidizing gas is usually humidified and then supplied to the catalyst layer.

Patent Document 3 discloses that in a methanol fuel cell that supplies methanol to the anode, the anode catalyst layer contains an anode catalyst including a fibrous supported catalyst using carbon fiber as a carrier and a granular supported catalyst using carbon particles as a carrier. However, it is described that the ratio of the fibrous supported catalyst in the anode catalyst on the surface facing the anode gas diffusion layer is higher than the ratio of the fibrous supported catalyst in the anode catalyst on the surface facing the electrolyte membrane. . At this time, it is proposed that the weight ratio of the electrolyte to the weight of the anode catalyst is 50 to 140% by weight on the surface facing the anode gas diffusion layer, and 150 to 250% by weight on the surface facing the electrolyte membrane. There is.

Patent Document 4 describes that in a polymer electrolyte fuel cell, composite particles in which catalyst particles are supported on conductive particles are contained in an amount of 20.000% by mass or more and 80.000% by mass or less, and a proton conductive polymer is contained in a proportion of 19.999% by mass. % or more and 60.000% by mass or less, and an electrode catalyst layer containing 0.001% by mass or more and 20.000% by mass or less of polytetrafluoroethylene. It is described that the equivalent weight (EW) of the proton conductive polymer is preferably 250 or more and 2000 or less, more preferably 250 or more and 800 or less.

JP2012-243431A Japanese Patent Application Publication No. 2004-247316 JP2009-117248A Japanese Patent Application Publication No. 2004-273257

As described above, in a fuel cell, fuel gas or oxidizing gas is humidified in order to reduce the resistance to proton movement. Therefore, it is necessary to provide equipment (humidifier) for generating water vapor gas and humidifying fuel gas or oxidizing gas separately from the fuel cell.

However, when a fuel cell is used for a mobile device such as a vehicle, it may not be possible to secure sufficient space for installing a humidifier. Therefore, a fuel cell that has high output performance under conditions of low humidification (eg, relative humidity of 20% to 40%) is desired.

In conventional fuel cells, when operated under low humidity conditions, the ionomer in the electrolyte membrane and catalyst layer dries out, increasing proton transfer resistance. As a result, output decreases. On the other hand, by increasing I/C in the catalyst layer, water retention can be increased and drying can be suppressed, but gas diffusivity is reduced. As a result, the output decreases.

One aspect of the present disclosure includes a first fibrous electrically conductive member, a first particulate electrically conductive member, a first catalyst particle, and a first proton conductive resin, and wherein the first The mass ratio I ₁ /C ₁ of the proton conductive resin is in the range of 1.0 to 1.6, and the ratio of the first fibrous conductive member to 100 parts by mass of the first particulate conductive member is 30 parts by mass. 50 parts by mass, and the EW value of the first proton conductive resin is 600 to 850.

Another aspect of the present disclosure relates to a fuel cell including a cathode having the cathode catalyst layer of the above aspect, an anode, and an electrolyte membrane interposed between the anode and the cathode.

According to the present disclosure, under low humidification operating conditions, it is possible to achieve both gas diffusivity and proton conductivity of the catalyst layer, and improve the power generation performance of the fuel cell.
While the novel features of the invention are set forth in the appended claims, the invention is further understood by the following detailed description, taken together with the drawings, both as to structure and content, as well as other objects and features of the invention. It will be well understood.

FIG. 1 is a cross-sectional view schematically showing the structure of a single cell of a fuel cell according to an embodiment of the present disclosure. 2 is a graph showing the results of measuring the logarithmic differential pore volume distribution of the cathode catalyst layers used in cell A1 of Example 1 and cells B1 to B3 of Comparative Examples 1 to 3 by mercury intrusion method.

The cathode catalyst layer of the fuel cell according to the embodiment of the present disclosure includes a fibrous conductive member (first fibrous conductive member), a particulate conductive member (first particulate conductive member), catalyst particles (first catalyst particles), and a proton conductive resin (first proton conductive resin). The cathode catalyst layer satisfies the following conditions (1) to (3).
(1) The ratio I ₁ /C ₁ of the mass of the first proton conductive resin to the mass of the first particulate conductive member is in the range of 1.0 to 1.6.
(2) The ratio of the first fibrous conductive member to 100 parts by mass of the first particulate conductive member is 30 to 50 parts by mass.
(3) The EW value of the first proton conductive resin is 600 to 850.
Here, the EW value means the mass (in grams) of the proton conductive resin in a dry state per mole of proton exchange groups (for example, sulfonic acid groups). The smaller the EW value, the larger the number of proton exchange groups occupying the proton conductive resin, and the lower the proton transfer resistance.

By increasing the ratio I ₁ /C ₁ of the mass of the first proton conductive resin to the mass of the first particulate conductive member, low proton transfer resistance can be obtained even under low humidification conditions due to the water retention effect. On the other hand, gas diffusivity decreases. However, by increasing the ratio of the first fibrous conductive member to the first particulate conductive member, it is possible to ensure a gas diffusion path even when I ₁ /C ₁ is high.

Conditions for low humidification include setting I ₁ /C ₁ in the range of 1.0 to 1.6 and setting the ratio of the first fibrous conductive member to 100 parts by mass of the first particulate conductive member to be 30 to 50 parts by mass. This is necessary in order to achieve both low proton transfer resistance and high gas diffusivity.

By increasing the proportion of the fibrous conductive member, the thickness of the catalyst layer tends to increase. As the thickness of the catalyst layer increases, proton movement resistance tends to increase. However, by using the first proton conductive resin having an EW value of 850 or less, the proton transfer resistance can be kept low even when the catalyst layer becomes thick due to the introduction of a fibrous conductive member.
On the other hand, the EW value of the first proton conductive resin is preferably 600 or more in view of ease of manufacturing the proton conductive resin.

Furthermore, it has been found that by using a resin with an EW value of 600 to 850 as the first proton conductive resin, proton transfer resistance can be lowered and gas diffusivity can be further improved. The EW value of the first proton conductive resin may be 600 to 850, 600 to 800, or 650 to 800.

As a result of measuring the distribution of pore diameter D of the catalyst layer by mercury porosimetry, it was found that the catalyst layer satisfying the above conditions (1) to (3) had a distribution of logarithmic differential pore volume dV/d (logD) of 0.006 μm. It may have a peak in the range of ~0.015 μm. Therefore, it is considered that the gas diffusivity is improved by forming a gas diffusion path through the micropores having a pore diameter of 0.006 μm to 0.015 μm.
Note that logD is a common logarithm of the pore diameter D (μm). The peak in the range of 0.006 μm to 0.015 μm may have a maximum peak value of 0.4 (cc/g·log μm) or more.

In the pore volume distribution, the volume of pores in the region where the pore diameter D is 0.006 μm to 0.015 μm may be 20% or more of the volume of the pores in the region where the pore diameter D is 0.006 μm to 0.2 μm.

The reasons for the formation of micropores are currently being elucidated and are not limited to the following, but the following points can be considered.
A proton conductive resin having an EW value of 600 to 850 has a large number of side chains having proton exchange groups and has a bulky structure. By mixing with the fibrous conductive material, a three-dimensional network in which the proton conductive resin and the fibrous conductive material are intertwined is formed, and this network forms a pore structure having micropores that allow gas diffusion. it is conceivable that.

The above-described catalyst layer has excellent gas diffusivity and is therefore suitable for use as a cathode catalyst layer provided on the cathode side of a fuel cell.

A fuel cell according to an embodiment of the present disclosure includes a cathode having the cathode catalyst layer described above, an anode, and an electrolyte membrane interposed between the cathode and the anode. The anode typically has an anode catalyst layer.

As with the cathode catalyst layer, the anode catalyst layer provided on the anode side includes a fibrous conductive member (second fibrous conductive member), a particulate conductive member (second particulate conductive member), and catalyst particles (second catalyst particles). ), and a proton conductive resin (second proton conductive resin). However, the materials and/or blending ratios of the fibrous conductive member, particulate conductive member, catalyst particles, and proton conductive resin in the anode catalyst layer do not need to be the same as those in the cathode catalyst layer, and may be changed as necessary. You may change it as appropriate.

In particular, when operating under low humidification conditions, the ratio I ₂ /C ₂ of the mass of the second proton conductive resin to the mass of the second particulate conductive member in the anode catalyst layer is set to The ratio of the mass of the first proton conductive resin to the mass of the member is preferably greater than I ₁ /C ₁ .

At the cathode, water is produced by reaction with an oxidizing gas. On the other hand, the anode, where water is not produced, tends to be in a drier, lower humidity environment than the cathode. However, by making I ₂ /C ₂ in the anode catalyst layer larger than I ₁ /C ₁ in the cathode catalyst layer, water generated at the cathode can be easily diffused to the anode side. As a result, further improvement in output can be expected under low humidification operating conditions.

The ratio of the second fibrous conductive member to 100 parts by mass of the second particulate conductive member is 30 to 60 parts by mass, and I ₂ /C ₂ is 1.2 to 2.5 (more preferably 1.4 ~2.5). This makes it easy to increase the humidity on the anode side, making it easy to obtain high output even under low humidification operating conditions.

Below, elements common to the catalyst layers (anode catalyst layer and cathode catalyst layer) will be explained in detail.

(fibrous conductive member)
Examples of the fibrous conductive member include fibrous carbon materials such as vapor grown carbon fiber (VGCF (registered trademark)), carbon nanotubes, and carbon nanofibers. The diameter D _F of the fibrous conductive member is not particularly limited, but is preferably 200 nm or less, more preferably 5 nm or more and 200 nm or less, and even more preferably 10 nm or more and 170 nm or less. In this case, a sufficient gas path can be secured while reducing the volume ratio of the fibrous conductive member in the catalyst layer, and gas diffusibility can be improved. The diameter D _F of the fibrous conductive member is determined by arbitrarily taking out 10 fibrous conductive members from the catalyst layer and averaging these diameters. The diameter is the length in the direction perpendicular to the length direction of the fibrous conductive member.

The length L _F of the fibrous conductive member is also not particularly limited, but is preferably 0.2 μm or more and 20 μm or less, more preferably 0.2 μm or more and 10 μm or less. In this case, the fibers are substantially linear, and at least a portion of the fibrous conductive member is oriented along the thickness direction of the catalyst layer, making it easy to ensure a gas diffusion path. The length L _F of the fibrous conductive member is the average fiber length, and is determined by arbitrarily taking out 10 fibrous conductive members from the catalyst layer and averaging the fiber lengths of these fibrous conductive members. It will be done. In addition, in the case of substantially straight fibers, the fiber length of the fibrous conductive member mentioned above means the length of a straight line when one end of the fibrous conductive member and the other end are connected by a straight line.

The fibrous conductive member may have a hollow space (hollow part) inside. In this case, both longitudinal ends of the fibrous electrically conductive member may be open in the catalyst layer. The fact that both longitudinal ends of the fibrous conductive member are open means that the hollow portion and the outside communicate with each other through the openings. That is, the openings at both ends of the fibrous conductive member are not blocked by either the electrolyte membrane or the gas diffusion layer, and gas can enter and exit from both ends.
The side wall of the fibrous conductive member having a hollow portion may be provided with a through hole that communicates the hollow portion with the outside. Catalyst particles can be arranged and immobilized on the side wall of the fibrous electrically conductive member so as to block at least a portion of the through hole. The catalyst particles supported on the side wall so as to block at least a portion of the through-hole can more efficiently contact the reaction gas, and the reaction efficiency of the catalyst layer can be greatly increased.

(Particulate conductive member)
The particulate conductive member is not particularly limited, but carbon black is preferred because it has excellent conductivity. Examples of carbon black include acetylene black, Ketjen black, thermal black, furnace black, and channel black. The particle size (or the length of the structure composed of a plurality of connected primary particles) is not particularly limited, and those conventionally used in catalyst layers of fuel cells can be used.

(Catalyst particles)
Catalyst particles are not particularly limited, but include Sc, Y, Ti, Zr, V, Nb, Fe, Co, Ni, Ru, Rh, Pd, Pt, Os, Ir, lanthanide series elements, and actinide series elements. Examples include catalytic metals such as selected alloys and simple substances. For example, the catalyst particles used in the anode include Pt, Pt-Ru alloy, and the like. Examples of the catalyst particles used in the cathode include Pt and Pt--Co alloy. At least a portion of the catalyst particles are supported on the particulate conductive member. In addition to the particulate conductive member, the catalyst particles may be supported on the fibrous conductive member. In this case, the catalyst particles can easily come into contact with the gas, and the efficiency of the gas oxidation reaction or reduction reaction can be increased.

On the other hand, a configuration in which catalyst particles are not substantially supported on the fibrous conductive member is also possible. That is, in the anode catalyst layer and/or the cathode catalyst layer, the catalyst particles may be substantially supported only on the particulate conductive member. The lower the catalyst supporting density of the fibrous conductive member, the higher the water repellency of the catalyst layer. Therefore, in this case, the drainage properties of the catalyst layer can be improved and the gas diffusivity can be enhanced. Here, the expression "substantially no catalyst particles are supported on the fibrous conductive member" refers to the following cases.
From an electron microscope photograph of the fibrous conductive member, the number i of catalyst particles supported on the fibrous conductive member is counted, and the number of catalyst particles supported on the fibrous conductive member per unit surface area of the fibrous conductive member is derived. do. Let S be the area occupied by the fibrous conductive member in the photograph. When the number i of catalyst particles is divided by S and the average of i/S is obtained for multiple areas (for example, 50 or more locations) in the photograph, it is determined from the average value of i/S that the number of catalyst particles supported on the fibrous conductive member is determined. The number of catalyst particles per surface area of the fibrous conductive member can be estimated. When the average value of i/S is 5 or less per 0.01 μm ² (that is, 5 or less in a square area of 100 nm on a side), catalyst particles are not substantially supported on the fibrous conductive member. It can be said that there is no.

From the viewpoint of immobilization of the catalyst particles, the diameter X of the catalyst particles is preferably 1 nm or more and 10 nm or less, more preferably 2 nm or more and 5 nm or less. When X is 1 nm or more, a sufficient catalytic effect by the catalyst particles can be obtained. When X is 10 nm or less, the catalyst particles are easily supported on the side walls of the particulate conductive member and the fibrous conductive member.

The diameter X of the catalyst particles is determined as follows.
For any one catalyst particle observed in a TEM image of the catalyst layer, the particle size (diameter of an equivalent circle) when the particle is considered to be spherical is calculated. This is performed for 100 to 300 catalyst particles observed in the TEM image, and the particle size of each is calculated. The average value of these particle sizes is defined as the diameter X of the catalyst particles.

(Proton conductive resin)
The proton conductive resin is not particularly limited, but examples include perfluorocarbon sulfonic acid polymers and hydrocarbon polymers. Among these, perfluorocarbon sulfonic acid polymers and the like are preferred because they have excellent heat resistance and chemical stability.

The proton conductive resin covers at least a portion of the fibrous conductive member and the catalyst particles. The proton conductive resin may further cover at least a portion of the particulate conductive member.

The proton conductive resin (first proton conductive resin) used in the cathode catalyst layer has an EW value of 600 to 850 in order to maintain low proton resistance even under low humidity operating conditions and improve gas diffusivity. things are used. Usually, a proton conductive resin having an EW value in the above range tends to aggregate when preparing a catalyst dispersion containing catalyst particles, a particulate conductive member, and a proton conductive resin in forming a catalyst layer. On the other hand, by mixing the fibrous conductive member and the proton conductive resin in the catalyst dispersion liquid at a blending ratio that satisfies the above conditions, aggregation of the proton conductive resin in the dispersion liquid can be suppressed, and the catalyst after coating and drying can be suppressed. In the layer, the proton conductive resin and the fibrous conductive member are intertwined to form micropores suitable for gas diffusion.

The thickness T of the catalyst layer is desirably as thin as possible from the viewpoints of downsizing the fuel cell, maintaining low proton resistance even under low humidity conditions, and obtaining high output. On the other hand, from the viewpoint of strength, it is preferable that it is not excessively thin. Generally, as the blending ratio of the fibrous conductive member increases, the thickness of the catalyst layer tends to increase.

The thickness T _C of the cathode catalyst layer may be, for example, 4 μm or more and 20 μm or less, or 4 μm or more and 10 μm or less. The thickness T _A of the anode catalyst layer may be, for example, 2 μm or more and 10 μm or less. The thicknesses T _C and T _A of the catalyst layer are average thicknesses, and straight lines are drawn along the thickness direction of the catalyst layer from one main surface to the other main surface at arbitrary 10 points in the cross section of the catalyst layer. It can be found by averaging the distances.

In the cathode catalyst layer, the supporting density D ₁ of the catalyst particles (first catalyst particles) supported on the particulate conductive member may be 20% to 50%. Similarly, in the anode catalyst layer, the supporting density D ₂ of the catalyst particles (second catalyst particles) supported on the particulate conductive member may be 20% to 50%. Note that the supported density D ₁ is the amount of the first catalyst particles supported on the first particulate conductive member that occupies the total mass of the first catalyst particles supported on the first particulate conductive member and the first particulate conductive member. is the proportion of the mass of The supporting density _D2 is the mass of the second catalyst particles supported on the second particulate conductive member, which occupies the total mass of the second catalyst particles supported on the second particulate conductive member and the second particulate conductive member. This is the percentage of

In the cathode catalyst layer, the ratio I ₁ /C ₁ of the mass of the proton conductive resin to the mass of the particulate conductive member is determined from the viewpoint of retaining moisture even under low humidification operating conditions and maintaining low proton resistance. It is preferable that ₁ /C ₁ be 1.0 or more. On the other hand, as I ₁ /C ₁ increases, pores are less likely to be formed and gas diffusivity tends to decrease, although it depends on the blending ratio of the fibrous conductive member. From the viewpoint of obtaining sufficient gas diffusivity, I ₁ /C ₁ is preferably 1.6 or less.

At the cathode, the reaction produces water. On the other hand, the anode, where no reaction water is produced, tends to be in a drier, lower humidity environment than the cathode. For this reason, the anode catalyst layer is required to have higher moisture retention than the cathode catalyst layer, and tends to require a higher I/C.
In the anode catalyst layer, the ratio I ₂ /C ₂ of the mass of the proton conductive resin to the mass of the particulate conductive member is determined from the viewpoint of retaining moisture even under low humidification operating conditions and maintaining low proton transfer resistance. I ₂ /C ₂ is preferably 1.2 or more, more preferably 1.4 or more. On the other hand, as I ₂ /C ₂ increases, the number of micropores in the catalyst layer decreases and gas diffusivity decreases. From the viewpoint of suppressing a decrease in gas diffusivity, I ₂ /C ₂ is preferably 2.5 or less.

From the viewpoint of maintaining low proton transfer resistance in the anode catalyst layer, I ₂ /C ₂ in the anode catalyst layer may be larger than I ₁ /C ₁ in the cathode catalyst layer. Thereby, water generated at the cathode can be easily diffused to the anode side, the moisture retention of the anode catalyst layer can be increased, and proton transfer resistance can be maintained low.

Regarding the blending ratio of the fibrous conductive member in the catalyst layer, the fibrous conductive member is contained in an amount of 30 parts by mass or more based on 100 parts by mass of the particulate conductive member in both the anode catalyst layer and the cathode catalyst layer. Diffusivity can be improved. On the other hand, when the blending amount of the fibrous conductive member is increased, the thickness of the catalyst layer becomes thicker, and the proton transfer resistance tends to increase. Moreover, cracks are likely to occur in the catalyst layer. From the viewpoint of suppressing an increase in proton transfer resistance and suppressing cracks, the amount of the fibrous conductive member in the cathode catalyst layer may be 50 parts by mass or less per 100 parts by mass of the particulate conductive member, In the anode catalyst layer, the amount may be 60 parts by mass or less based on 100 parts by mass of the particulate conductive member.

The catalyst layer is produced, for example, as follows.
First, catalyst particles and particulate conductive members are mixed in a dispersion medium (eg, water, ethanol, propanol, etc.). Next, while stirring the resulting dispersion, a proton conductive resin and a fibrous carbon material are sequentially added to obtain a catalyst dispersion. The proton conductive resin may be added in two or more parts. In this case, the second and subsequent additions of the proton conductive resin may be performed together with the fibrous carbon material. Thereafter, a catalyst layer is obtained by applying the obtained catalyst dispersion liquid to a uniform thickness on the surface of an electrolyte membrane or a suitable transfer base sheet and drying it.

Examples of the coating method include conventional coating methods such as a spray method, a screen printing method, and a coating method using various coaters such as a blade coater, knife coater, and gravure coater. As the transfer base sheet, it is preferable to use, for example, a sheet having a smooth surface such as polyethylene terephthalate (PET) or polypropylene. When using a transfer base sheet, the obtained catalyst layer is transferred to an electrolyte membrane or a gas diffusion layer, which will be described later.

Transfer of the catalyst layer to the electrolyte membrane or gas diffusion layer is performed by bringing the surface of the catalyst layer facing the transfer base sheet into contact with the electrolyte membrane or gas diffusion layer. By bringing the smooth surface of the catalyst layer into contact with the electrolyte membrane or gas diffusion layer, the interfacial resistance with the catalyst layer is reduced and the performance of the fuel cell is improved. The catalyst dispersion may be applied directly to the electrolyte layer.

An example of the structure of the fuel cell according to this embodiment will be described below with reference to FIG. 1. FIG. 1 is a cross-sectional view schematically showing the structure of a single cell arranged in a fuel cell according to an embodiment. Usually, a plurality of single cells are stacked and arranged in a fuel cell as a cell stack. In FIG. 1, one single cell is shown for convenience. The fuel cell according to this embodiment uses hydrogen (H ₂ ) as fuel.

The unit cell 200 has an electrolyte membrane 110, a first catalyst layer 120A and a second catalyst layer 120B arranged to sandwich the electrolyte membrane 110, and an electrolyte through the first catalyst layer 120A and the second catalyst layer 120B, respectively. The membrane electrode assembly 100 includes a first gas diffusion layer 130A and a second gas diffusion layer 130B arranged to sandwich a membrane 110 therebetween. Furthermore, the single cell 200 includes a first separator 240A and a second separator 240B that sandwich the membrane electrode assembly 100 therebetween. One of the first catalyst layer 120A and the second catalyst layer 120B functions as an anode, and the other functions as a cathode. A gas containing hydrogen (H ₂ ) can be supplied to the anode via the gas flow path 260A or 260B. Since the electrolyte membrane 110 is one size larger than the first catalyst layer 120A and the second catalyst layer 120B, the peripheral edge of the electrolyte membrane 110 protrudes from the first catalyst layer 120A and the second catalyst layer 120B. The peripheral edge of the electrolyte membrane 110 is sandwiched between a pair of seal members 250A and 250B.

One of the first catalyst layer 120A and the second catalyst layer 120B is an anode catalyst layer, and the other is a cathode catalyst layer. Here, the second catalyst layer 120B is an anode catalyst layer. In this case, the first catalyst layer 120A is a cathode catalyst layer, and the configurations of the first fibrous conductive member, the first particulate conductive member, and the first proton conductive resin satisfy the above conditions (1) to (3). Satisfied. As the second catalyst layer 120B, which is the anode catalyst layer, _a known material and _{a known} configuration can be adopted, and the second fibrous conductive member, the second _particle The above-described structure of the anode catalyst layer containing the conductive member and the second proton conductive resin can be preferably adopted.

(electrolyte membrane)
As the electrolyte membrane 110, a polymer electrolyte membrane is preferably used. Examples of materials for the polymer electrolyte membrane include the polymer electrolytes exemplified as proton conductive resins. The thickness of the electrolyte membrane is, for example, 5 to 30 μm.

(Gas diffusion layer)
The first gas diffusion layer 130A and the second gas diffusion layer 130B may have a structure with a base material layer or may have a structure without a base material layer. Examples of structures having a base layer include a structure having a base layer and a microporous layer provided on the catalyst layer side. A conductive porous sheet such as carbon cloth or carbon paper is used for the base layer. For the microporous layer, a mixture of a water repellent resin such as a fluororesin, a conductive carbon material, and a proton conductive resin (polymer electrolyte) is used.

(Separator)
The materials of the first separator 240A and the second separator 240B are not particularly limited as long as they have airtightness, electronic conductivity, and electrochemical stability. As such materials, carbon materials, metal materials, etc. are preferable. The metal material may be coated with carbon. For example, the first separator 240A and the second separator 240B are obtained by punching a metal plate into a predetermined shape and subjecting it to surface treatment.

In this embodiment, a gas flow path 260A is formed on the surface of the first separator 240A that comes into contact with the first gas diffusion layer 130A. On the other hand, a gas flow path 260B is formed on the surface of the second separator 240B that comes into contact with the second gas diffusion layer 130B. The shape of the gas flow path is not particularly limited, and may be formed into a straight type, serpentine type, or the like.

(Seal member)
The seal members 250A, 250B are made of an elastic material and prevent fuel and/or oxidizer from leaking from the gas flow paths 260A, 260B. The seal members 250A and 250B have, for example, a frame shape that surrounds the peripheral edges of the first catalyst layer 120A and the second catalyst layer 120B in a loop shape. As the seal members 250A and 250B, known materials and known configurations can be used, respectively.

Hereinafter, the present disclosure will be described in more detail based on examples. However, the present disclosure is not limited to the following examples.

[Example 1]
<Preparation of dispersion liquid for cathode catalyst layer>
A particulate conductive member (carbon black) carrying catalyst particles (Pt--Co alloy) was added to an appropriate amount of water, and the mixture was stirred and dispersed. After adding an appropriate amount of ethanol to the resulting dispersion while stirring, 40 parts of the fibrous conductive member (vapor-grown carbon fiber, average diameter 150 nm, average fiber length 10 μm) was added to 100 parts by mass of the particulate conductive member. A catalyst dispersion liquid for a cathode catalyst layer was prepared by adding parts by mass and 100 parts by mass of a proton conductive resin (perfluorocarbon sulfonic acid polymer, EW value 700) and stirring.

<Preparation of dispersion liquid for anode catalyst layer>
A particulate conductive member (carbon black) carrying catalyst particles (Pt) was added to an appropriate amount of water, and the mixture was stirred and dispersed. After adding an appropriate amount of ethanol to the resulting dispersion while stirring, 40 parts of the fibrous conductive member (vapor-grown carbon fiber, average diameter 150 nm, average fiber length 10 μm) was added to 100 parts by mass of the particulate conductive member. and 120 parts by mass of a proton conductive resin (perfluorocarbon sulfonic acid polymer, EW value 900) were added and stirred to prepare a catalyst dispersion for an anode catalyst layer.
I ₁ /C ₁ =1.0 in the cathode catalyst layer, and I ₂ /C ₂ =1.2 in the anode catalyst layer.

<Preparation of single cell>
Next, two PET sheets were prepared. Using the screen printing method, the obtained catalyst dispersion for the cathode catalyst layer was applied to the smooth surface of one PET sheet in a uniform thickness, and the obtained catalyst dispersion liquid for the cathode catalyst layer was applied to the smooth surface of the other PET sheet. A catalyst dispersion liquid for an anode catalyst layer was applied to a uniform thickness. Thereafter, it was dried to form two catalyst layers. The thickness of the cathode catalyst layer was 7 μm, and the thickness of the anode catalyst layer was 3 μm.

The obtained catalyst layers were transferred onto both main surfaces of an electrolyte membrane having a thickness of 15 μm to form a cathode on one surface of the electrolyte membrane and an anode on the other surface. Further, two porous conductive carbon sheets were prepared as gas diffusion layers, and one was brought into contact with the anode and the other with the cathode.

Next, a frame-shaped seal member was placed to surround the anode and cathode. A test single cell A1 was completed by sandwiching the entire cell between a pair of stainless steel flat plates (separators) having a gas flow path in the portion in contact with the gas diffusion layer.

<Evaluation>
The power generation performance of the single cell A1 of Example 1 was evaluated. Specifically, the single cell A1 was heated to 80° C., and fuel gas (H ₂ ) with a relative humidity of 20 to 40% was supplied to the anode, and oxidant gas (air) with a relative humidity of 20 to 40% was supplied to the cathode. . The fuel gas and the oxidant gas were supplied at a cell inlet gas pressure of 40 to 120 kPa. Then, the voltage (initial voltage) V, resistance value R, and power density P of the single cell A1 are controlled while controlling the load control device so that the current flows constantly, and changing the current density with respect to the electrode area of the anode and cathode. It was measured.

[Example 2]
For 100 parts by mass of particulate conductive member, 30 parts by mass of fibrous conductive member (vapor grown carbon fiber, average diameter 150 nm, average fiber length 10 μm), and proton conductive resin (perfluorocarbon sulfonic acid polymer, A catalyst dispersion liquid for a cathode catalyst layer was prepared by adding 100 parts by mass (EW value: 700) and stirring.

Except for this, a catalyst dispersion liquid for an anode catalyst layer was prepared in the same manner as in Example 1, and a test single cell A2 was completed.
In the single cell A2, I ₁ /C ₁ in the cathode catalyst layer is 1.0.

[Example 3]
For 100 parts by mass of particulate conductive member, 40 parts by mass of fibrous conductive member (vapor grown carbon fiber, average diameter 150 nm, average fiber length 10 μm), and proton conductive resin (perfluorocarbon sulfonic acid polymer, A catalyst dispersion liquid for a cathode catalyst layer was prepared by adding 100 parts by mass (EW value: 850) and stirring.

Other than this, a catalyst dispersion liquid for an anode catalyst layer was prepared in the same manner as in Example 1, and a test single cell A3 was completed.
In the single cell A3, I ₁ /C ₁ in the cathode catalyst layer is 1.0.

[Comparative example 1]
In preparing the dispersion liquid for the cathode catalyst layer, a perfluorocarbon sulfonic acid polymer having an EW value of 900 was used as the proton conductive resin.
For 100 parts by mass of particulate conductive member, 20 parts by mass of fibrous conductive member (vapor grown carbon fiber, average diameter 150 nm, average fiber length 10 μm), and proton conductive resin (perfluorocarbon sulfonic acid polymer, A catalyst dispersion liquid for the cathode catalyst layer was prepared by adding 120 parts by mass (EW value: 900) and stirring.

Except for this, a catalyst dispersion liquid for an anode catalyst layer was prepared in the same manner as in Example 1, and a test single cell B1 was completed.
In the single cell B1, I ₁ /C ₁ in the cathode catalyst layer is 1.2.

[Comparative example 2]
In preparing the dispersion for the cathode catalyst layer, no fibrous conductive member was added.
A catalyst dispersion liquid for the cathode catalyst layer is prepared by adding 120 parts by mass of proton conductive resin (perfluorocarbon sulfonic acid polymer, EW value 900) to 100 parts by mass of the particulate conductive member and stirring. did.

Except for this, a catalyst dispersion liquid for an anode catalyst layer was prepared in the same manner as in Comparative Example 1, and a test single cell B2 was completed.
In the single cell B2, I ₁ /C ₁ =1.2 in the cathode catalyst layer.

[Comparative example 3]
For 100 parts by mass of particulate conductive member, 20 parts by mass of fibrous conductive member (vapor grown carbon fiber, average diameter 150 nm, average fiber length 10 μm), and proton conductive resin (perfluorocarbon sulfonic acid polymer, A catalyst dispersion liquid for the cathode catalyst layer was prepared by adding 120 parts by mass (EW value: 700) and stirring.

Except for this, a catalyst dispersion liquid for an anode catalyst layer was prepared in the same manner as in Example 1, and a test single cell B3 was completed.
In the single cell B3, I ₁ /C ₁ =1.2 in the cathode catalyst layer.
[Comparative example 4]
For 100 parts by mass of particulate conductive member, 20 parts by mass of fibrous conductive member (vapor grown carbon fiber, average diameter 150 nm, average fiber length 10 μm), and proton conductive resin (perfluorocarbon sulfonic acid polymer, A catalyst dispersion liquid for a cathode catalyst layer was prepared by adding 100 parts by mass (EW value: 700) and stirring.

Except for this, a catalyst dispersion liquid for an anode catalyst layer was prepared in the same manner as in Example 1, and a test single cell B4 was completed.
In the single cell B4, I ₁ /C ₁ in the cathode catalyst layer is 1.0.

Table 1 shows the results of measuring the maximum output density of cells A1 to A3, B1, and B4. The maximum output density is shown as a relative value when the maximum output density of cell B4 is set to 100.

In cell B1, the EW value of the first proton conductive resin exceeds 850, and the blending ratio of the first fibrous conductive member to the first particulate conductive member is less than 30% by mass, so the output density is low. Furthermore, in cell B1, at a current density of 1.4 A/cm ² or more, the output voltage decreased and power generation was not possible. In contrast, cells A1 to A3 were able to operate at current densities up to 2.6 A/cm ² . In cells A1 to A3, a maximum output density more than twice that of cell B1 was obtained.

Cells A1 to A3 and B4 have the same first proton conductive resin and the same value of I ₁ /C ₁ , but differ in the blending ratio of the first fibrous conductive member to the first particulate conductive member. From Table 1, in cells A1 and A2 in which the blending ratio of the first fibrous conductive member to the first particulate conductive member is 30% by mass or more, the blending ratio of the first fibrous conductive member to the first particulate conductive member is 20% by mass or more. The output characteristics are significantly improved compared to cell B4 of % by mass.

FIG. 2 shows the pore diameter D of the logarithmic differential pore volume dV/d (logD) obtained by mercury intrusion method for the cathode catalyst layers used in cell A1 of Example 1 and cells B1 to B3 of Comparative Examples 1 to 3. The results of measuring the distribution depending on are shown.

In cell B1 of Comparative Example 1 and cell B2 of Comparative Example 2, some logarithmic differential pore volume exists in the range of 0.006 μm to 0.015 μm. However, since the EW value of the first proton conductive resin exceeds 850, no clear peak appears within the above range. In addition, in cell B3 of Comparative Example 3, the EW value of the first proton conductive resin is 850 or less, but the blending ratio of the first fibrous conductive member to the first particulate conductive member is less than 30% by mass. , no peak is observed in the range of 0.006 μm to 0.015 μm.

[Examples 4 to 7]
In preparing the catalyst dispersion for the anode catalyst layer, the amount of proton conductive resin added was changed from Example 1.
The amount of proton conductive resin (perfluorocarbon sulfonic acid polymer, EW value 900) added to 100 parts by mass of the particulate conductive member was 140 parts by mass, 160 parts by mass, 180 parts by mass, and 200 parts by mass, respectively. A catalyst dispersion liquid for the anode catalyst layer was prepared.

Other than this, test single cells A4 to A7 were completed in the same manner as in Example 1. A4 to A7 are Examples 4 to 7, respectively. Cells A4 to A7 were evaluated in the same manner as in Example 1.
In cells A4 to A7, I ₂ /C ₂ in the anode catalyst layer is 1.4, 1.6, _1.8 , and _2.0 , respectively.

Table 2 shows the results of measuring the maximum output density of cells A4 to A7. The maximum output density is shown as a relative value when the maximum output density of cell A1 is set to 100. High output was obtained in all of cells A1 and A4 to A7 under low humidification operating conditions. In particular, cells A4 to A7 with I ₂ /C ₂ of 1.4 or more have a remarkable degree of improvement in output compared to cell A1 with I ₂ /C ₂ of 1.2.

[Examples 8 to 10]
In preparing the catalyst dispersion liquid for the anode catalyst layer, the proton conductive resin and the amount added thereof were changed from Example 1.
Anode catalyst layer in which the amount of proton conductive resin (perfluorocarbon sulfonic acid polymer, EW value 780) added was 120 parts by mass, 140 parts by mass, and 160 parts by mass, respectively, with respect to 100 parts by mass of the particulate conductive member. A catalyst dispersion was prepared.

Other than this, test single cells A8 to A10 were completed in the same manner as in Example 1. A8 to A10 are Examples 8 to 10, respectively. Cells A8 to A10 were evaluated in the same manner as in Example 1.
In cells A8 to A10, I ₂ /C ₂ in the anode catalyst layer is I ₂ /C ₂ =1.2, 1.4, and 1.6, respectively.

Table 3 shows the results of measuring the maximum output density of cells A8 to A10. The maximum output density is shown as a relative value when the maximum output density of cell A1 is set to 100.

The fuel cell according to the present disclosure can be suitably used as a power source for a stationary household cogeneration system or a power source for a vehicle. The present disclosure is suitable for application to polymer electrolyte fuel cells, but is not limited thereto, and can be applied to fuel cells in general.
Although the invention has been described in terms of presently preferred embodiments, such disclosure is not to be construed as a limitation. Various modifications and alterations will no doubt become apparent to those skilled in the art to which this invention pertains after reading the above disclosure. It is, therefore, intended that the appended claims be construed as covering all changes and modifications without departing from the true spirit and scope of the invention.

100: membrane electrode assembly, 110: electrolyte membrane, 120: catalyst layer, 120A: first catalyst layer, 120B: second catalyst layer, 130A: first gas diffusion layer, 130B: second gas diffusion layer, 200: fuel Battery (single cell), 240A: first separator, 240B: second separator, 250A, 250B: seal member, 260A, 260B: gas flow path

Claims (4)

comprising a first fibrous conductive member, a first particulate conductive member, a first catalyst particle, and a first proton conductive resin,
The ratio I ₁ /C ₁ of the mass of the first proton conductive resin to the mass of the first particulate conductive member is in the range of 1.0 to 1.6,
The ratio of the first fibrous conductive member to 100 parts by mass of the first particulate conductive member is 30 to 50 parts by mass,
The first proton conductive resin has an EW value of 600 to 850 ,
The distribution of the logarithmic differential pore volume dV/d (logD) measured by mercury intrusion method shows that the pore diameter D is in the range of 0.006 μm to 0.015 μm (however, in the range of 0.01 μm or more and 0.015 μm or less). ) , the cathode catalyst layer has a peak. A cathode having the cathode catalyst layer according to claim 1 ;
an anode;
A fuel cell comprising: an electrolyte membrane interposed between the cathode and the anode. The anode has an anode catalyst layer,
The anode catalyst layer includes a second fibrous conductive member, a second particulate conductive member, second catalyst particles, and a second proton conductive resin,
The fuel cell according to claim 2 , wherein a ratio _I2 / _C2 of the mass of the second proton conductive resin to the mass of the second particulate conductive member is greater than _I1 / _C1 . The anode catalyst layer is
The ratio of the second fibrous conductive member to 100 parts by mass of the second particulate conductive member is 30 to 60 parts by mass,
The fuel cell according to claim 3 , wherein the I ₂ /C ₂ is 1.2 to 2.5.

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